Magnesium batteries offer the potential of good capacity and lower cost in comparison to state-of-art lithium-ion batteries, due to the divalency and relative abundance of magnesium. A challenge in the development of magnesium batteries has been in the development of electrolytes that support reversible magnesium stripping/deposition and that are stable against electrode corrosion within desired electrical potential windows.
Common magnesium salts, as well as polar aprotic solvents, generally do not support reversible magnesium stripping/deposition because they decompose at the magnesium anode surface creating a layer that is impermeable to magnesium ions. Grignard reagents and magnesium organohaloaluminates have been shown to support reversible magnesium stripping/deposition, but are corrosive to non-noble metal cathodic current collectors at electrical potentials greater than about 2.5 V (vs. Mg/Mg2+), thus limiting their usefulness. More recently, electrolytes based on magnesium borohydride or magnesium salts of boron cluster anions (including carboranyl anions) have shown the ability to support reversible magnesium stripping/deposition, with high oxidative stability at electrical potentials exceeding 3.5 V (vs. Mg/Mg2+) in some cases without inducing corrosion to non-noble metal cathodic current collectors.
Nearly all such electrolytes contain an ether solvent, as ethers are the only solvents known to be compatible with magnesium metal. However ethers typically undergo electrochemical oxidation at about 3.5 V (vs. Mg/Mg2+). For this reason, ether solvents can become a limiting factor in the electrochemical stability of an electrolyte composition when utilized in combination with a magnesium salt, such as several mentioned above, that is characterized by high (e.g. greater than 3.0 V vs. Mg/Mg2+) electrochemical stability.